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Peanut insect control is changing

As peanut growers ready themselves for another production year, they'll find a few changes as far as recommendations and new materials for insect control are concerned, says Ron Weeks, Auburn University Extension entomologist.

“The main change is the addition of Dimilin to our list of peanut insecticides this year,” says Weeks. “This can be helpful for some growers, and if you produce cotton, you're already familiar with the product. It's an insecticidal growth regulator. Obviously, it's not a broad-spectrum type of insecticide — and it doesn't provide a quick contact kill.”

For peanut growers, Dimilin offers some protection at the end of the season for insects such as the velvet bean caterpillar, he says. “If you've grown soybeans before, you might have used it at the end of the season for velvet bean caterpillars and loopers. It's more of a preventative than a curative treatment,” says Weeks.

In peanuts, especially in past seasons, some producers in Alabama have seen a generation of velvet bean caterpillars moving in at about mid-August. “And particularly lately, since we've carried our harvest season into November in the past couple of years, we've seen more of these insects moving in. And if we have an extended season, they will continue to move north,” he says.

On peanuts, Dimilin also will work to some degree on other foliage feeders such as corn earworms and fall armyworms, although it is not generally recommended for a threshold population of fall armyworms in peanuts.

“We generally say that if we make those preventative applications starting around 95 to 100 days after the peanuts reach full-size growth, they quit putting on new foliage. We put out an application and maybe make a repeat application about two to three weeks later. We've seen a reduction in foliage loss on peanuts from a minimum of about 10 to 15 percent just for the lower limbs. And in some areas where you have high populations of velvet bean caterpillars, you can reduce the foliage loss by about 50 percent,” says Weeks.

Some growers, he adds, get busy at the start of peanut digging season, and the worms move into fields. “As they're moving from one field to another, growers forget to scout their fields. Then, they'll go into a field to look at it and check for maturity and find it already has been defoliated. Peanuts don't invert very well when they don't have leaves on them,” he says.

The Extension Service, says Weeks, is recommending Dimilin for foliage feeders. “On the label, you'll also find lesser cornstalk borers and a couple of other things, but we're not recommending this material for those. We've looked at Dimilin for five or six years — repeat application during the season in dry years and in non-irrigated fields — and we haven't seen a yield enhancement or an effect on lesser cornstalk borers,” he says.

There is a three application maximum of 24 ounces per acre for Dimilin, says Weeks. “For most velvet bean caterpillar control, the 2 to 4-ounce rate is all you need,” he adds.

Mustang and Mustang Max also are labeled for use on peanuts now, says Weeks. The products are similar to pyrethroids such as Karate that already are labeled on peanuts, he says. Performance is about the same and the insects controlled are about the same as the other peanut pyrethroids, he says.

Consero is a combination material that was labeled last year for peanuts and other crops, he says. It is a combination of Prolex and Tracer. This is a two-container mix with maximum rates of 1.5 ounces for the Prolex component and 2 ounces for the spinosad or Tracer component.

“If you get into high populations of some of the hard-to-kill worms like loopers or beet armyworms, this will be a good product for those situations,” says Weeks.

Another change that occurred this past summer was a Section 2ee label for Lorsban 15G in the Southeastern states, he says. “It basically allows a sequential application. We already were allowed the maximum rate of material for Lorsban. If you have an extended drought period, and populations of lesser cornstalk borers are coming in quicker, the previous label might have allowed a second or third generation to hit you before you could re-apply. This allows a minimum of 10 days up to a 30-day period after the first application to repeat it if you're in an extended drought or if the lesser cornstalk borer generations are out there.”

The three-cornered alfalfa hopper has become a hot topic in peanut production in recent years, says Weeks, and no one seems to be able to come up with a reason for their increasing severity.

“There's one opinion that changing from conventional to conservation-tillage has caused this insect to be more of a problem. Also, the fact we're using other at-plant insecticides might be a factor. In trials where I've compared Temik and Thimet for thrips control, Temik is giving us longer residual control and we're having better control against three-cornered alfalfa hoppers in our Temik plots compared to our Thimet plots.

“Thimet is giving us lower levels of tomato spotted wilt virus in some cases, but Temik is giving us longer residual control and it's controlling three-cornered alfalfa hoppers. We're seeing more Thimet used for thrips control and that may be why we're seeing more three-cornered alfalfa hoppers.”

The University of Georgia, explains Weeks, has done away with the threshold treatment levels for three-cornered alfalfa hoppers in peanuts. Previous recommendations called for treating if you found one per 6 foot of row more than 75 days until harvest or one per 3 foot of row 25 to 75 days before harvest. You didn't need to treat at all if you were at about 25 days to one month before harvest.

“Last year, they discovered this was not a workable threshold because they were treating throughout the season, and at the end of the season, they were not seeing that much damage in some of those situations. So we're going back to square one. We recommend that you treat based on the number of three-cornered alfalfa hoppers — what I call an active infestation. If you're seeing girdled stems in June or July, maybe up until the first of August, you probably need to treat. And if you're seeing immatures out there, you'll probably get enough damage from them and the adults that you need to make an application.

“Basing treatments just on adults in some cases may be reasonable, but these insects are so mobile, they fly in and out of the field, and it depends on the time of the day whether or not they'll be there. It also depends on what is around the field as far as refuges. It's difficult to determine.”